Sputter etching for selective removal of material from the surface of substrates, particularly those used for microelectronics apparatus, is already in considerable use. The practice is, in effect, a reversal of the previously well-known art of sputter deposition and involves simply a reversal of roles so that the target being etched replaces the customary source of material being deposited. Sputter etching has numerous advantages and particularly is regarded as enabling a high degree of definition when applied to selective removal processes using suitable masking layers of material which are more impervious to sputter etching and therefore protect underlying material. In particular, sputter etching generally involves a particle or ion beam incident perpendicularly upon the substrate surface. For many configurations, this provides a satisfactory result with relatively sharply defined perpendicular sidewalls as defined by the masking layer particularly where the material being removed is part of, or overlies, a layer of uniform thickness and where the portion being removed has a lateral, or width, dimension, which is large relative to its height. Because it is in the nature of the sputter etching process for redeposition of sputtered material to occur, there is a tendency in the case of patterns having narrow line widths to form virtual steps as a consequence.
Thus, where the topography of the patterned material on a substrate, typically a semiconductor body, comprises underlying layers having different thicknesses so that the underlying layer includes steps from one level to another, as well as for patterns having narrow line widths, the usual sputter etch procedure does not remove overlying material completely from the inside corners of the pattern. Consequently subsequent depositions and material removals depart from the desired degree of pattern definition as a consequence of such inadequate etching procedure.
Accordingly, an object of this invention is a method for insuring more complete removal of unmasked material by sputter etching.